Revision 2 Texture, Geochemistry And
Total Page：16
File Type：pdf, Size：1020Kb
This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press. DOI: https://doi.org/10.2138/am-2021-7889. http://www.minsocam.org/ P a g e | 1 1 Revision 2 2 3 Texture, geochemistry and geochronology 4 of titanite and pyrite: Fingerprint of 5 magmatic-hydrothermal fertile fluids in 6 the Jiaodong Au province 7 8 Xing-Hui Li1,2, Hong-Rui Fan1,2,3,*, Ri-Xiang Zhu2,3,4, Matthew Steele- 5 1,2,3 6 9 MacInnis , Kui-Feng Yang , Cai-Jie Liu 10 11 1Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, 12 Chinese Academy of Sciences, Beijing 100029, China 13 2Innovation Academy for Earth Science, Chinese Academy of Sciences, Beijing 14 100029, China 15 3College of Earth and Planetary Science, University of Chinese Academy of 16 Sciences, Beijing 100049, China 17 4State Key Laboratory of Lithospheric Evolution, Institute of Geology and 18 Geophysics, Chinese Academy of Sciences, Beijing 100029, China 19 5Department of Earth and Atmospheric Sciences, University of Alberta, 20 Edmonton, AB T6G 2E3, Canada 21 6No. 6 Institute of Geology and Mineral Resources Exploration of Shandong 22 Province, Zhaoyuan 265400, China 23 24 *Corresponding author. Tel.: +86 10 82998218; fax: +86 10 62010846. E-mail 25 address: [email protected] (H.-R., Fan). Always consult and cite the final, published document. See http:/www.minsocam.org or GeoscienceWorld This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press. DOI: https://doi.org/10.2138/am-2021-7889. http://www.minsocam.org/ P a g e | 2 26 ABSTRACT 27 The Au mineralization in the giant Jiaodong Au province is enigmatic and 28 difficult to fit current classic mineralization models, primarily because of 29 uncertainties as to the sources of ore-forming fluids and metals. The ca. 120 Ma 30 Au mineralization has been previously proposed to have occurred during a 31 magmatic lull, which would negate a magmatic-hydrothermal genetic model. 32 However, recent drilling has revealed a buried mineralized monzonite 33 equivalent in age to the Au mineralization, in the Linglong goldfield. Here, we 34 present comprehensive textural, geochemical (LA-(MC)-ICPMS trace element, 35 Nd and S isotopes) and geochronological (LA-ICPMS U-Pb dating) analyses of 36 titanite and pyrite from this previously unrecognized monzonite. Three types of 37 titanite were distinguished, including magmatic Ttn1 and hydrothermal Ttn2 38 and Ttn3, which show indistinguishable U-Pb ages (120.7 ± 3.1 Ma and 120.9 39 ± 2.6 Ma), REE patterns and Nd isotopes (εNd(t) = -14.7 to -12.9), implying that 40 hydrothermal fluids were directly exsolved from the monzonitic magma, 41 contemporaneous with the large-scale Au mineralization at ca. 120 Ma. The Nd 42 isotopes of titanite potentially indicate a lower crustal source mixed with mantle 43 materials for the monzonite. Four types of pyrite were analyzed, including 44 magmatic Py1 from the fresh biotite monzonite, hydrothermal Py2 from the 45 altered biotite monzonite, hydrothermal Py3 from quartz-pyrite veins with a 46 monazite U-Pb age of 118.2 ± 4.6 Ma, and magmatic Py4 from mafic enclaves 47 of the Gushan granite at ca.120 Ma. The d34S values of magmatic Py1 and Py4 Always consult and cite the final, published document. See http:/www.minsocam.org or GeoscienceWorld This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press. DOI: https://doi.org/10.2138/am-2021-7889. http://www.minsocam.org/ P a g e | 3 48 (+1.9 to +6.3 ‰, and +5.0 to +6.4 ‰, respectively) and hydrothermal Py2 and 49 Py3 (+6.4 to +9.5 ‰, and +6.5 to +7.6 ‰, respectively) are consistent with 50 sulfur isotopic fractionation between melt and fluid. Hydrothermal Py2 and Py3 51 also have higher Co, As, Ag, Sb and Bi contents and submicron gold inclusions, 52 implying that the magmatic-hydrothermal fluids were fertile for mineralization. 53 This study highlights the importance of monzonite magmatism and exsolved 54 fertile fluids in regional Au mineralization. Hydrous magmas at ca.120 Ma 55 probably extracted Au efficiently from the lower crustal-mantle sources and 56 released auriferous fluids at the late magmatic stage, leading to the formation 57 of Au deposits in the Jiaodong province. 58 Keywords: Titanite, pyrite, monazite, biotite monzonite, U-Pb geochronology, 59 magmatic-hydrothermal fluid 60 Always consult and cite the final, published document. See http:/www.minsocam.org or GeoscienceWorld This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press. DOI: https://doi.org/10.2138/am-2021-7889. http://www.minsocam.org/ P a g e | 4 61 INTRODUCTION 62 The Early Cretaceous Au deposits in the Jiaodong Peninsula constitute the 63 largest Au province of China, containing more than 5000 tons of proven Au 64 resources. Mineralization in the Jiaodong Peninsula is considered unique 65 relative to the accepted model for orogenic Au deposits (e.g., Groves et al., 66 1998), in that Au mineralization postdates the Precambrian metamorphic 67 wallrocks by about 2 billion years (Goldfarb and Santosh 2014). Numerous 68 studies have defined the ore-controlling structures, hydrothermal alterations, 69 ore-fluid chemistry, hydrothermal processes and fluid evolution of both 70 disseminated- to stockwork-style and auriferous quartz-pyrite vein-type Au 71 deposits across the Jiaodong Peninsula (Fan et al. 2003, 2007; Li et al. 2012a; 72 Goldfarb and Santosh 2014; Mills et al. 2015; Deng et al. 2015, 2020b; Feng et 73 al. 2018, 2020; Li et al. 2018). The timing of Au mineralization has also been 74 well constrained to 120 ± 5 Ma by Rb-Sr dating of pyrite, 40Ar/39Ar dating of 75 hydrothermal muscovite and U-Pb dating of hydrothermal monazite (Yang and 76 Zhou 2001; Ma et al. 2017; Li et al. 2018; Zhang et al. 2020; Deng et al. 2020a). 77 Nevertheless, the genesis of the Jiaodong Au province is contentious, given the 78 failure of current models of mineralization to account for its features. This 79 debate is primarily rooted in uncertainties as to the sources of ore-forming fluids 80 and metals, and particularly their genetic relationship(s) to Mesozoic 81 magmatism, Precambrian metamorphic host rocks, subducted slab and 82 sediment, and/or metasomatized lithosphere (Zhai et al. 2004; Chen et al. 2005; Always consult and cite the final, published document. See http:/www.minsocam.org or GeoscienceWorld This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press. DOI: https://doi.org/10.2138/am-2021-7889. http://www.minsocam.org/ P a g e | 5 83 Goldfarb and Santosh 2014; Zhu et al. 2015; Deng et al. 2015, 2020b; Wang et 84 al. 2020). 85 Two main problems obstruct linking Au mineralization to the widespread 86 granitic magmatism in the Jiaodong Au province. Firstly, a time gap of at least 87 ~8 million years separates the ages of mineralization and of known magmatism 88 (Li et al. 2019a; Deng et al. 2020a). Secondly, direct evidence for a genetic 89 affinity between magmatism and hydrothermal mineralization has been hitherto 90 lacking. However, recent deep drilling projects in the Linglong goldfield, one 91 of the largest Au-producing districts in the Jiaodong Au province, discovered a 92 buried mineralized biotite monzonite that shows petrographic features distinct 93 from those of the exposed Mesozoic granitoids (Linglong, Luanjiahe, 94 Guojialing and Aishan granites). Shen et al. (2016) constrained the 95 emplacement age of the monzonite to ca. 124 Ma by 40Ar/36Ar dating of biotite, 96 and suggested a temporal relationship between the monzonite and Au 97 mineralization. The monzonite is nearly contemporaneous with the regional 98 Gushan granite, which has a zircon U-Pb age of 120-119 Ma (Li et al. 2012b). 99 Thus, this newly discovered monzonite suggests a potentially extensive episode 100 of magmatism during this period. Moreover, the mineralized monzonite shows 101 distinctive hydrothermal features, suggesting a relationship between magmatic- 102 hydrothermal fluids and mineralization. As such, the mineralized monzonite 103 provides a good opportunity to evaluate the role of magmatism and magmatic- 104 hydrothermal fluid release in the ore-forming process, and to explore the Always consult and cite the final, published document. See http:/www.minsocam.org or GeoscienceWorld This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press. DOI: https://doi.org/10.2138/am-2021-7889. http://www.minsocam.org/ P a g e | 6 105 sources of ore-forming fluids and metals, in the Jiaodong Au province. 106 Several magmatic-hydrothermal minerals are present in the monzonite, 107 including titanite, monazite, pyrite, pyrrhotite and magnetite. Titanite 108 commonly contains sufficient uranium contents for precise U-Pb dating and has 109 been widely used to date magmatic and hydrothermal events (Frost et al. 2001; 110 Li et al. 2010; Xiao et al.